Why hasn't your company got an exemption from the CAA to:-
"fly closer than 500ft to any person, vessel,vehicle or structure whilst flying over Great Britain for the purpose of photographic or geophysical survey".
The company I work for has this and has to follow various restrictions such as informing the police and recording the times of such low flying along with CANP iaw the UK Air Pilot ENR 1.10 - Flight planning.
You wouldn't then have to worry about what clearance a Mil Unit gives you.
HF